I'm sure many readers are aware of the BBC's 2007 advertisement (released, of course, on April Fools Day!) showing flying penguins. It was developed to advertise the corporation's (then-new) BBC Player software, allowing viewers to stream TV programs to their computers. In case you missed it, here it is.
I was intrigued to find this 'how they did it' background look at the advertisement. Here's how they made it.
Looks like a lot of work went into it - but the result was pretty convincing.